Prostate cancer is the most commonly diagnosed cancer and the second leading cause of cancer-related mortality in men. Prostate cancer is responsible for over 80 deaths per day in the US, almost uniformly due to complications associated with metastasis. Understanding this metastatic propensity is of paramount clinical importance and critical to developing new therapies. The androgen receptor (AR) is a key gene involved in prostate cancer biology. AR-V7 is an alternatively spliced variant that lacks the ligand-binding domain. Importantly, expression of AR-V7 is associated with both therapeutic resistance and metastatic disease. Therefore, understanding the mechanism of AR-V7 creation and its contribution to metastatic disease is of high clinical significance and will lead to the development of new therapeutic targets. Objective: The goal of this proposal is to elucidate the mechanisms of upstream AR-V7 synthesis and downstream AR-V7 signaling, both of which may lead to new therapeutic strategies in prostate cancer. We hypothesize that induction of an epithelial-to-mesenchymal transition (EMT) alters AR transcription and alternative splicing leading to an increase in AR-V7 expression and AR-V7 signaling feeds-forward to promote a drug-resistant and highly metastatic cancer. Specific aims: We propose to: (1) examine the mechanism by which EMT induces AR-V7 expression; (2) unravel the mechanism(s) by which AR-V7 functionally impacts epithelial plasticity; and (3) measure and correlate the proportion of patients that express AR-V7 and EMT biomarkers in circulating tumor cells from metastatic prostate cancer patients progressing on AR-targeted therapies. Study design: For aim 1, we will systematically dissect the mechanisms of the transcriptional regulation and alternative splicing of AR-V7 during EMT induction. For aim 2, we will identify novel AR-V7-specific targets, measure the functional impact of AR-V7 both in vitro and in vivo on migration, invasion and metastasis and determine the mechanism by which AR-V7 induces distinct-targets involved in promoting metastatic disease. For aim 3, we will utilize AR-V7 status and RNA-seq data to measure and correlate AR-V7 expression with EMT biomarkers from circulating tumor cells isolated longitudinally from metastatic prostate cancer patients. Cancer relevance: The success of this research plan will advance the field of metastatic prostate cancer by identifying unique candidates to target AR-V7-driven prostate cancer and lead to the discovery of markers that can be measured clinically to better select successful treatments for prostate cancer patients. By providing insights into the molecular understanding of AR-V7-driven prostate cancer, this proposed research is directly relevant to the mission to eliminate cancer as a major health problem.